Conventional audio-visual presentation systems, such as cinemas and home entertainment systems, typically display video content of an audio-visual presentation (e.g. a film, a TV show or a commercial, for example) to a viewer on a screen (e.g. a cinema or TV screen), and play audio content of the audio-visual presentation (e.g. a film soundtrack) to the viewer through a speaker system. The problem of synchronising playback of the audio and video content of an audio-visual presentation in the form of a film (or “motion picture”) was solved in the early part of the 20th century by placing a soundtrack encoding the audio physically onto the tape of the film reel, next to the frames of the film, in order to ensure that the right moment of audio accompanies the right moment in the video when the reel is played. Despite the many technological advances that have occurred since that time, the concept underlying this approach to synchronising picture and sound has remained widely in use.
Recently, there has been great interest in developing audio-visual presentation systems that allow each viewer of a film or other kind of audio-visual presentation to enjoy a personalised auditory experience, by listening to one of a number of alternative soundtracks via headphones or earphones, for example. The soundtrack may be selected by each viewer in accordance with their individual needs or preferences. For example, each viewer might wish to listen to one of a number of alternative language versions of a film, descriptive audio for the visually impaired, or a director's commentary. Such delivery of audio content to viewers also opens up the possibility of using binaural audio presentation to immerse each viewer in a realistic 3D sound environment that is difficult to replicate using even the most advanced surround sound speaker systems available today.
However, known approaches to delivering personalised audio content to viewers have significant drawbacks that have hindered their uptake. For example, in the case of delivering personalised audio content to viewers in a cinema via headphones that plug into headphone jacks provided in cinema seats, a significant investment in the required infrastructure and its maintenance must be made by the cinema. An alternative approach which has been proposed, namely of streaming the audio content (for example, via a WiFi™ network or a Bluetooth™ connection provided by the cinema) to a portable device, such as the cinema-goer's smart-phone or PDA, so that the cinema-goer can listen to the film's audio content via headphones or earphones connected to his/her portable device, is also costly as the cinema would need to provide an appropriate means of reliably distributing the audio content throughout the cinema auditorium during shows.